7 Replies Latest reply on Nov 21, 2011 6:07 AM by user_78878863

    Amux with ADCs

    glenn.stroz

       Hi,

         

      I'm attempting to emulate a multi channel ADC using PSoC 5. I have it set up using a Amux Sequencer with the output leading to the Delta Sigma ADC. I've tried setting the ADC to run in multisample mode and stopping the conversions before switching the channels. I then switch the channels and start the conversions again. When I do this, I get the same result for both channels. That is, I always get the result from channel 0, not channel 1 - even if I say "next channel". 

         

      However, if I set the Delta Sigma ADC to continuously run and add a 100 us delay after the channel switch then I see the correct output. 

         

      Is there some know bug for using an Amux with the ADCs? The amux data sheet does not list a settling time or any necesssary information. Any suggestions? My goal is to get the period as low as possible, so have a delay is not ideal.

         

       

         

      Thanks

        • 1. Re: Amux with ADCs
          ki.leung

          Here is a code example

             
             

           http://www.cypress.com/?rID=38799

             
             

          Donwload the exmaple and play with it, see how it was used.

             
          • 2. Re: Amux with ADCs
            glenn.stroz

             Thank you for the example code. I was able to get it working in my setup. I just had to add a wait for conversion to complete function to get the appropriate results.

               

            Now that I have this working with the delta sigma ADC, would it be possible to have a similar setup with the SAR ADCs? They don't seem to support multi sample mode or anything related to switched inputs. Can anyone comment on the steps necessary to have the SAR ADCs hooked up  to an AMUX and give accurate results? Now that I've seen the accuracy of the Delta Sigma ADC I want to see the speed comparison with the same setup on the SAR ADCs. 

            • 3. Re: Amux with ADCs
              ki.leung

              Here is what to do

                 

              select channel with MUX;

                 

              start SAR ADC;

                 

              while not complete{};

                 

              read adc value;

                 

               

                 

              I normaly not use the continous mode, as I can control when to start the conversion. 

                 

              One thing you should know that there is a bug in the initilization of the SAR of PSoC5, (I think it is same bug in PSoC 3). Can not  remember what exatly it is. May be someone in Cypress would help here. Otherwise wait until next monday when I'm back to the office.

              • 4. Re: Amux with ADCs
                gautam.das.g

                Hi gstroz,

                   
                   

                 

                   
                   

                SAR ADC supports sampling rate of upto 700 kSPS.

                   
                   

                At this rate, it is advisable to use DMA to do the transfer. A code example is available which explains the Hardware multiplexing of SAR ADC.

                   
                   

                Link to the Code Example is http://www.cypress.com/?rID=47003

                   
                   

                 

                   
                   

                The End Of Conversion (EOC) signal of SAR ADC is used to trigger the DMA transfer.

                • 5. Re: Amux with ADCs
                  user_78878863

                  IIRC there is a bug(?) with the PSoC5 ES1. It prevents using the Delta-Sigma-ADC the same as the SAR ADC with respect to interfacing the AMuxHw. The second example shows how the SAR ADC can be used to automatically switch between multiple channels, using the EOC signal. This doesn't work with the DelSigADC, here the switch has to be made in software, since the EOC signal somehow cannot be used to switch to the next mux channel 8but I forgot the details).

                  • 6. Re: Amux with ADCs
                    dushyant.bansiwal

                     Dear H L,

                       

                    can u repost the link, it seems that its been relocated; its no longer available @  http://www.cypress.com/?rID=38799

                       
                         please check and update.   
                       
                            
                       
                        thanks in advance.   
                    • 7. Re: Amux with ADCs
                      user_14586677

                      There is an example project in Creator, use link on Start Page,

                         

                      "Find Example Project" -